Microstructure and properties of DD6 single crystal superalloy repaired joint using laser melting deposition

Laser melting deposition is more suitable for repairing thin-walled substrates of single crystal alloys compared to argon arc welding and micro plasma arc welding. This article used laser melting deposition technology for additive repair of DD6 single crystal superalloy. The microstructure characteristics of the repaired zone and heat affected zone of the additive repaired joint were analysed by optical microscopy， scanning electron microscopy， and EBSD. And the microhardness distribution and high-temperature tensile properties of the repaired joint were tested. The results indicate that in the heat affected zone adjacent to the repair interface， γ' phase is partially coarsened and dissolved， and the hardness decreases significantly. The microstructure of repaired zone is an oriented columnar crystal structure grown epitaxially， and composed of γ+γ' phase and a small amount of dispersed carbides between dendrites. Many elongated columnar stray grains remain in the repaired zone， mostly distribute near the fusion line. As the height of the repaired zone increases， the dendrite spacing and hardness of the epitaxial growth tissue increases gradually， and the proportion of fine grid γ' phase in the dendrites increases continuously. The tensile strength of the repaired joint at 980 ℃ reaches 102% of the base material， and the yield strength reaches 92% of the base material， but the elongation is relatively poor.